Traditionally, nomographs have been used to solve multivariable equations for an unknown variable when two or more variables are known. A traditional nomograph has a number of scaled axes, each axis representing one of the variables in an equation. The axes of a traditional nomograph are in parallel and each of these scaled axes are calibrated and arranged so that a straight line drawn through all of the axes will intersect a value on each axis that will satisfy the equation. When two or more variables of the equation are known, a traditional nomograph can be used to solve for the third variable by drawing a line through the axes representing two known variables intersecting the values of the two known variables. The line will then intersect the remaining axis representing the unknown variable and this intersection will indicate the value of the unknown variable.
Before the advent of computers and calculators nomographs were popular because they allowed a person to determine an unknown variable of an equation without doing extensive manual calculations. All a person had to do to determine a third related value using a traditional nomograph was to lay a ruler on the nomograph so that the ruler intersect the two know values and read the value where the ruler crosses the remaining axis. These traditional nomographs were especially useful to allow lay people to “solve” complex equations without requiring mathematical calculations.
Although nomographs are easy to use and do not require any calculations, they are often labor intensive to construct because each axis must be calibrated and located relative to the other axes.
Another disadvantage of traditional nomographs is that the answers found using a nomograph often lacks precision. Depending on the size and accuracy of the scale on the axis, the precision of the resulting answer will be dependent upon how well the two known variables are intersected and to what degree the resulting answer can be read. Also, if a variable has units of measurement, one axis is required for each different unit of measure.
With the advent of pocket calculators and computers, nomographs are no longer needed to solve complex equations, it is much simpler and more precise to use a simple computer program to solve an equation rather then rely on how accurate a value can be read off an intersection of an axis. As a result, nomographs for solving equations have fallen out of fashion. Computers and pocket calculators are more than up to the task of doing the calculations necessary to solve for a related unknown variable when the other variables are known and can often do it just as fast and with much greater precision.
While computers and pocket calculators can solve a multivariable equation for an unknown variable just as fast, if not faster, and with more precision than a traditional nomograph, the calculations and relationships between the variables remain invisible to the user. The user is not able to see a visual representation of the relationship of the variables and is not easily able to determine the sensitivity of the equation to the different variables. Also, using a computer to solve for an unknown variable in an equation does not easily allow a user to see how altering the different variables of the equation can affect the relationship of the related variables and often makes it much harder for a user to “tweak” the different variables to arrive at satisfactory values for the equation.